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Potassium Nitrate

Science EncyclopediaScience & Philosophy: Positive Number to Propaganda - World War Ii

Potassium nitrate, also known as saltpeter or niter, is a chemical compound consisting of potassium, nitrogen, and oxygen. While it has many applications, including use as a fertilizer, its most important usage historically has been as a component of gunpowder. Over time its use as an explosive has been made nearly obsolete by dynamite and TNT, but it is still used today in artilleryshell primers, hand-grenade fuses, and fireworks.

Potassium nitrate consists of three basic chemical elements: potassium a soft, light, silver white metal; nitrogen a colorless, odorless gas; and oxygen, another common gas. When these three elements are reacted in the proper proportions they form a whitish compound known as nitre, or saltpeter, which has the chemical formula KNO3. This naturally occurring compound, which forms thin whitish glassy crusts on rocks, can be found in sheltered areas such as caves and particularly on soils rich in organic matter. Until the first World War the United States imported most of its potassium nitrate from Europe where it was mined from ancient sea beds. When these sources became unavailable during the war, the brines lakes in California became the principal supplier of nitre.

Since it is rich in potassium, an element which is vital for plant growth, large quantities of potassium nitrate are used annually as fertilizer. It also has utility as a food preservative, and although never proven, it is claimed that when ingested saltpeter has an aphrodisiac, or sexual-desire-reducing effect. However, the most renowned use for this whitish powder was discovered over 2,200 years ago by the Chinese. When 75% potassium nitrate is mixed appropriately with 15% carbon (charcoal) and 10% sulfur, the resultant black powder has explosive properties. This mixture (which throughout history has enjoyed such colorful nicknames as "Chinese Snow" and "the Devil's Distillate") eventually became known as gunpowder. As early as A.D. 1000, it was used by its inventors in explosive grenades and bombs. By the thirteenth century, the use of gunpowder had spread throughout the western world: in 1242 the English philosopher Roger Bacon described his own preparation of this material. By the early fourteenth century, black powder and guns were being manufactured in Europe. Although the early firearms were awkward and inefficient, they were rapidly improved. Their use led to significant social changes, including the end of the European feudal system. In fact, it is arguable that exploitation of the properties of gunpowder has been responsible for many of the major social and cultural changes in history.

Originally, potassium nitrate and the other components of gunpowder were carefully hand mixed and broken into small particles using wooden stamps. Later, water power mechanized the stamping stage, and metal stamps replaced the wooden ones. In modern production, charcoal and sulfur are mixed by the tumbling action of steel balls in a rotating hollow cylinder. The potassium nitrate is pulverized separately, and the ingredients are then mixed and ground. After further crushing the gunpowder is pressed into cakes; these are then rebroken and separated into grains of specific size. Finally, the grains are tumbled in wooden cylinders to wear off rough edges. During this process graphite is introduced, a coating powder which provides a friction-reducing, moisture-resistant film.

By 1900 black powder had been virtually replaced as the standard firearms propellant. Although it had served for centuries, it had many drawbacks. It produced a large cloud of white smoke when ignited, built up a bore-obstructing residue after relatively few shots, and absorbed moisture easily. Its replacement, nitrocellulose based smokeless powders (known as guncotton), eliminated most of these disadvantages. Gunpowder had already been largely replaced as a primary blasting explosive by dynamite and TNT but it is still widely used today in artillery-shell primers, hand-grenade fuses, and fireworks.

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